MAXIMUM USEABLE FREOUENCY
(MUF)- LOWEST USEABLE FREOUENCY (LUF). ' Each layer of the ionosphere has a frequency that is the highest that the layer will reflect. The exact frequency is determined by the amount of ions in the layer. As seen in fig 5. the lower frequencies are reflected by the lower layers while the higher frequencies enetrate the lower layers and are reflected back by the higher layers. To cover the largest tactical area of operations possible the highest frequency that will reflect should be used since the higher the reflecting layer the wider the area covered by the reflection (see fig 5.). Since the ionosphere is always changing a general rule when in manual
operation is to select a frequency 15% lower than the actual MUF to avoid problems. This frequency is called the frequency of optimum traffic (FOT). Signals on frequencies that exceed the MUF go through the ionosphere and are lost in outer space.
The MUF is also different for different angles of reflection. Signals on lower takeoff angles can utilize higher frequencies for communications because they will be reflected. The ALE mode of THFRS will automatically prevent signals with a frequency above the MUF from being selected for operations. ALE will select the best radio frequency for communications on a continuous basis if used. A limitation of HF radio is the high radio noise (static) level on HF frequencies. Radio noise comes from sources in outer space, lightning in the earth's atmosphere, and man-made sources. Noise on a particular system depends mainly on location and season.
(MUF)- LOWEST USEABLE FREOUENCY (LUF). ' Each layer of the ionosphere has a frequency that is the highest that the layer will reflect. The exact frequency is determined by the amount of ions in the layer. As seen in fig 5. the lower frequencies are reflected by the lower layers while the higher frequencies enetrate the lower layers and are reflected back by the higher layers. To cover the largest tactical area of operations possible the highest frequency that will reflect should be used since the higher the reflecting layer the wider the area covered by the reflection (see fig 5.). Since the ionosphere is always changing a general rule when in manual
operation is to select a frequency 15% lower than the actual MUF to avoid problems. This frequency is called the frequency of optimum traffic (FOT). Signals on frequencies that exceed the MUF go through the ionosphere and are lost in outer space.
The MUF is also different for different angles of reflection. Signals on lower takeoff angles can utilize higher frequencies for communications because they will be reflected. The ALE mode of THFRS will automatically prevent signals with a frequency above the MUF from being selected for operations. ALE will select the best radio frequency for communications on a continuous basis if used. A limitation of HF radio is the high radio noise (static) level on HF frequencies. Radio noise comes from sources in outer space, lightning in the earth's atmosphere, and man-made sources. Noise on a particular system depends mainly on location and season.